The characters that were lacking were Ratchet and Ironhide. They got the shaft in every single movie. I don't even think Ratchet talked this movie and if he did I don't remember as it would have been one short sentence.

I disagree about Ironhide. I think he was given a good amount of screentime in the first film, and he definitely had a presence (although brief) in the second film. He didn't have much screentime in the third film, but the Mexican standoff scene more than made up for it and gave him one last defining moment before he was killed. Not to mention he had a handful of memorable lines throughout the three films, like:

"You feelin' lucky, punk?"
"I just wanted to show 'em my cannons."
"You have a rodent infestation. Shall I terminate?"
"The parents are very irritating. Can I take them out? I'm just sayin' we could. It's an option."
"Punkass Decepticon."
"You want a piece of me? I will tear you apart!"
"Prime, make something of yourself! He's pissed."
"Class dismissed."

I'll agree with you regarding Ratchet, though. I feel like the only movie where he actually did anything was the first one, and even then all he did was get a good one-liner ("The boy's pheromone levels suggest he wants to mate with the female"), walk into some electric wires, and cut off Brawl's arm with his wrist cutter thing. He had probably two lines in ROTF and maybe three or four in DOTM. I feel like the only reason why they had Ratchet go to Chernobyl and then the moon with Optimus was because they had just remembered that Ratchet was still in these movies. If he had died, it wouldn't have had nearly the same impact as Ironhide's death.

All in all, though, the only Autobots who have a substantial amount of screentime throughout the three films are Optimus and Bumblebee. It makes sense from a story standpoint, as they are the main two that the audience has a connection to, especially Bee. But both times I saw DOTM, people did react to Ironhide's death.